The direction of air flow into or out of a room depends on the pressure of the room relative to its adjacent spaces. The differential pressure between the room and the adjacent spaces need only be slight, practically immeasurable, to create air flow. Rooms such as hospital operating rooms, patient isolation rooms, sterilization rooms, research laboratories, clean rooms, etc., often require directional air flow. For example, a patient isolation room, containing a patient who is susceptible to infection, is supplied with highly filtered air under positive pressure, i.e., clean air flows out of the room at all times, thereby preventing dirty or infectious air from entering the room. This is accomplished by supplying clean air to the patient's room at a greater flow rate than the rate at which air is exhausted from the room. Conversely, if the patient is infectious or the room contains toxins, the room should be kept under negative pressure, i.e., the rate at which potentially contaminated air is exhausted from the room is greater than the rate at which new air is supplied to the room.
In the above described environments, it is important that the proper direction of air flow be maintained. If the proper direction or air flow ceases, a detecting element should indicate the improper situation. In some instances, an alarm may be activated until the pressure condition in the room can be corrected.
Transducers are currently available that measure the differential pressure between a room and reference space and use of the resulting measurement for alarm actuation. A problem associated with these types of differential pressure sensors is that the room must be well sealed or "tight" in order to build up a measurable pressure. When a door or window is open for an appreciable period of time, the differential pressure of the room approaches zero causing the sensor to falsely actuate the alarm, despite the presence of directional air flow into or out of the room. Accordingly, there is a need for a device which can detect the directional air flow into or out of a room without relying on differential pressure measurements.
Another type of transducer currently available utilizes a "hot wire" anemometer to detect the directional velocity of air. Such transducers are an improvement over a differential pressure transducer. However, their accuracy is dependent upon the sensitivity and proper calibration of the transduction element and the associated processing circuitry.
Further, since neither air pressure nor air velocity can be seen, people often hang a piece of string or tissue in a doorway or in front of a vent to assess the direction of air flow into or out of a room and to verify the results of either differential pressure or anenometer-type transducer.
U.S. Pat. Nos. 2,808,580, Fuller; 3,192,470, Wadey; 3,689,908, Ray; 3,820,396, Gamer et al.; 4,486,744, Pratt et al.; 4,774,676, Stenzel et al.; and 4,963,857, Sackett; all disclose devices for detecting the presence and velocity of a fluid, typically a gas. However, none of these references disclose a device which allows the desired flow direction of a fluid to be selected and which actuates an alarm when the detected direction is other than the desired direction.
Accordingly, there exists a need for a device which allows the desired direction of air flow to be selected and visually monitored, and/or, which actuates an alarm when the detected direction is other than the one selected.
It is therefore an object of this invention to provide a device for detecting the presence and direction of air flow between two rooms or a room and its adjoining spaces.
Another object of the present invention is to provide a device which allows the desired direction of air flow to be selected.
A further object of the present invention is to provide a device which indicates when the detected direction of air flow is different from the selected direction of air flow.
Still another object of the present invention is to provide a device for detecting the presence and direction of air flow between a room and its adjoining spaces which does not require that the room be well sealed, i.e., at near zero differential pressure.
A further object of the present invention is to provide a device for detecting the presence and direction of air flow whose accuracy does not depend primarily on the sensitivity and calibration of the transducer and associated processing circuitry.
Yet another object of the present invention is to provide a device for detecting presence and direction of air flow which allows for direct visual confirmation of the direction of air flow.